This invention relates to an image formation method of a serial printer comprising heads each having a plurality of print elements for completing an image by performing the print operation more than once, an image formation control system for controlling the image formation of the serial printer, and an image formation system for forming an image.
FIG. 2 is an illustration to show a schematic configuration of an example of a general serial printer. In the figure, numeral 1 denotes a carriage drive motor, numeral 2 denotes a timing belt, numeral 3 denotes a recording head, numeral 4 denotes a carriage, numeral 5 denotes an ink tank, numeral 6 denotes a carriage guide, numeral 7 denotes a cable, numeral 8 denotes recording paper, numeral 9 denotes a paper feed motor, and numeral 10 denotes a feed roll. Here, an ink jet printer is shown as a serial printer example.
The carriage 4, which has the recording heads 3 mounted thereon, slides the carriage guides 6 and reciprocates in the horizontal scanning direction of arrow H in the figure. The carriage 4 is moved by the timing belt 2 driven by the carriage drive motor 1. In the example, two recording heads 3 are arranged in the move direction of the carriage 4.
The cable 7 is introduced into the recording heads 3 for supplying power to a heater in the recording heads and transmitting a signal to a drive circuit. The ink tanks 5 are attached to the recording heads 3 for supplying color inks. A plurality of nozzles are placed in each recording head 3 for jetting supplied ink to the recording paper 8 for recording. The recording paper 8 is driven by the feed roll 10 rotated by the paper feed motor 9 in the arrow P direction in the figure for vertical scanning. For the vertical scanning, in addition to such a method of moving the recording paper 8, a method of moving the carriage 4 in the vertical scanning direction, a method of moving both the recording paper 8 and the carriage 4 relatively, or the like is available.
A 2-head printer comprising a color head and a black head placed side by side on a carriage in the horizontal scanning direction each head having a plurality of print elements arranged in the vertical scanning direction as a recording head configuration in a serial printer has been developed as shown in FIG. 3, which is a schematic drawing to show an example of recording heads used with the 2-head printer. In FIG. 3, numeral 11 denotes a black head and numeral 12 denotes a color head. For example, in an ink jet system, nozzles are arranged in each recording head longitudinally in the figure. The black head 11 performs black recording with all or some of the arranged nozzles.
The nozzles arranged in the color head 12 are separated into groups in response to the number of used ink colors. Here, three color inks of cyan, magenta, and yellow are used and the nozzles for jetting their respective color inks are arranged in line. In FIG. 3, BK denotes black, C denotes cyan, M denotes magenta, and Y denotes yellow. The nozzle groups for jetting different color inks are spaced from each other for preventing colors from being mixed on the head face. Of course, any other color ink may be used.
In such a recording head, the number of nozzles that can print black differs from that of nozzles that can print a color other than black. To use such a recording head for printing, a black image can be printed with the black head width as a unit, thus can be printed at high speed. However, a color image can be printed only with the one-color width of the nozzles placed in the color head as a unit at the maximum. Normally, once the color mode is set, even a black area is printed only in color image print units. Thus, if an original with color and black areas mixed contains a black area that can be printed at high speed, high-speed print is not performed and the print speed lowers relatively.
To solve such a problem, whether the print object is color or black is determined and the print method is changed in response to whether the image to be printed is color or black, for example, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 8-238805. Thus, to print an original with color and black areas mixed, a black area is printed at high speed by making full use of the black head width, so that high-speed print is enabled as a whole.
On the other hand, a method of forming an image by horizontally scanning a single area more than once is used as one of recording methods. The number of horizontal scanning times is called the number of print divisions. If the number of print divisions is two, only 50% print is performed by executing horizontal scanning once, and 100% print is performed by executing horizontal scanning twice. Paper is fed half of the one-color print width of the color head or the whole print width of the black head between the first horizontal scanning and the second horizontal scanning. FIG. 4 is an illustration of an example of a print image formed by executing horizontal scanning twice; it shows only one color or black and only several dots. First, in print scanning shown in FIG. 4A, image data is thinned out 50% to prepare print data and the print data is printed. Here, assume that the dots indicated by ◯ are printed. After the dots are printed, a relative move in the vertical scanning direction is made half of the print width of the color. In print scanning shown in FIG. 4B, print data of a pattern complementing the dots printed in FIG. 4A is prepared and printed. Here, the dots indicated by X are printed. Then, 100% print is complete as in the area at the middle stage shown in FIG. 4C. Such split print is performed for 100% print by executing horizontal scanning more than once, whereby misalignment of print scanning joints caused by a paper feed error and dot position misalignment caused by directivity variations in nozzles can be made inconspicuous and adjacent dots printed at the same time can be decreased for lessening bleeding for improving the image quality.
In the Unexamined Japanese Patent Application Publication No. Hei 8-238805, such split print in color mode is described, but such a print method in black mode is not used. To perform such split print in the black mode, the following problem occurs at the mode change time:
FIG. 5 is an illustration of the problem at the mode change time when split print is executed. Here, the number of print divisions is two. In FIG. 5, area A shown on the left is an area that can be printed only in black and area B is an area printed in color. Assume that recording heads exist at the position in the vertical scanning direction shown in (1) in the figure. In the next horizontal scanning, the tips of the heads are moved to line b and horizontal scanning is executed in the state in (2) in the figure. The first horizontal scanning of the area between lines a and b is executed. In this state, horizontal scanning of the area between lines a and b needs to be executed once more. If print is continued intact in the black mode, a relative move of the recording heads is made to the position in the vertical scanning direction shown in (3) in the figure and the second horizontal scanning of the area between lines a and b is executed.
However, at the position shown in (3) in the figure, the top of the area B is exceeded for the color of the color head at the bottom stage in the figure. Thus, if a transition to the color mode is made from the position and an attempt is made to execute color print, the color area between lines b and c (area C) cannot be printed in the color of the color head at the bottom stage in the figure. Thus, when the transition is made from the black mode to the color mode, a blank area as large as the print-impossible area is required.
This also applies when the transition is made from the color mode to the black mode; horizontal scanning is executed only once over the area of half of the black head width from the end line of the color mode and a desired density cannot be obtained. Thus, a blank area as large as the area is required.
A similar problem may also occur in cases other than the mode change between the color mode and the black mode. For example, a similar problem to that in FIG. 5 occurs in change between modes different in the number of print divisions because the modes differ in recording width. An area where horizontal scanning cannot be executed as many times as the number of print divisions occurs at the upper and lower end of a recording medium, and a margin as large as the area is required at the top and bottom of the recording medium.
To solve such a problem, the following recording method is possible, for example, in mode change between color and black modes: FIG. 6 is a schematic representation of a specific example of the operation at the change time from the black mode to the color mode in related art. In FIG. 6, the heads shown in FIG. 3 are used and the number of print divisions is two. The head portions used for print are hatched. In the example shown in FIG. 6, black characters and the hatched color portion are mixed.
Since a color image does not exist in the upper part of the image to be recorded, first the black mode is used for recording. Horizontal scanning is executed at the position in (1) in FIG. 6 and the first printing of the area between a line a and the line immediately preceding a line b is executed with the lower half of the black head. A move in the vertical scanning direction is made by half of the black head, then the whole black head is used for executing horizontal scanning at the position in (2) in FIG. 6, whereby the second printing of the area between the line a and the line immediately preceding the line b and the first printing of the area between the line b and the line immediately preceding a line c are executed.
Color data exists on a line d. This line d is assumed to be a mode change point. Change to the color mode is made at this mode change point. Before the transition to the color mode is made, the area between the line a and the line immediately preceding the line d is printed in the black mode for completing the image. A move in the vertical scanning direction is made to the line immediately preceding the line d and the black head is used for executing horizontal scanning at the position in (3) in FIG. 6, whereby the second printing of the area between the line b and the line immediately preceding the line c and the first printing of the area between the line c and the line immediately preceding the line d are executed.
In this state, the second printing of the area between the line c and the line immediately preceding the line d is not yet executed. Then, as shown in (4) in FIG. 6, horizontal scanning is again executed at the same position without changing the position in the vertical scanning direction, whereby the second printing of the area between the line c and the line immediately preceding the line d is executed and the printing in the black mode is terminated. At this point in time, the mode is changed to the color mode and the image on the line d and the later lines may be formed in the color mode.
In the color mode, while a move in the vertical scanning direction is made every half of the one-color print width of the color head, horizontal scanning is executed twice for the same area for forming a color image. For example, on the lines of the line d to the line immediately preceding a line e, printing is executed in the color corresponding to the lower end (top) of the color head in the figure in horizontal scanning in (5) and (6) in FIG. 6. After this, printing is executed in other colors in overlapped relation and an image can be formed in various colors.
FIG. 7 is a schematic representation of a specific example of the operation at the change time from the color mode to the black mode in related art. In this example, color data runs out on a line f and only monochrome data exists on the later lines. Thus, the line f is set to a mode change point and the lines immediately preceding the line f are printed in the color mode, then the mode is changed from the color mode to the black mode on the line f and the lines following the line f are printed in the black mode.
A color image to the line immediately preceding the line f in (1) to (10) in FIG. 7 is formed by performing the color mode operation described above. After horizontal scanning at the position in (10) in FIG. 7, a move in the vertical scanning direction is made so that the rear end of the black head is placed on the line f. The mode is changed from the color mode to the black mode, then recording is executed in the black mode. However, if the recording operation is performed in the black mode as it is, the area between the line f and the line immediately preceding a line i is printed only once. Then, the first printing of the area between the line f and the line immediately preceding the line i is executed at the position in (11) in FIG. 7 and the second printing of the area between the line f and the line immediately preceding the line i and the first printing of the area between the line i and the line immediately preceding a line k are executed at the position in (12) in FIG. 7, the same position as in (11) in FIG. 7. After this, printing may be executed in the normal black mode.
Thus, when the mode is changed from the black mode to the color mode, horizontal scanning is executed as many times as the number of print divisions at the same vertical scanning position before the mode is changed, and the image in the record area is completed in the black mode, then the mode is changed to the color mode. When the mode is changed from the color mode to the black mode, the image in the record area is completed in the color mode, then the mode is changed to the black mode and horizontal scanning is executed as many times as the number of print divisions at the same vertical scanning position only at the first time, then printing is executed in the normal black mode. The operation at the mode change time is thus performed, whereby the need for placing a blank area in the vicinity of the mode change point as described above is eliminated and smooth mode change can be made.
Likewise, for the change operation between modes different in record width, the mode is changed at a mode change point, then horizontal scanning is executed more than once at the same vertical scanning position, whereby smooth mode change can be made, for example, as described in the Unexamined Japanese Patent Application No. Hei 7-237321.
On the other hand, to record in a margin of a recording medium, a warp in the margin of the recording medium, etc., may cause the recording medium to come into collision with a moving head or the distance between the head and the recording medium to change, causing disorder in an image. To avoid this, recording is not executed in a state in which the margin of the recording medium exists in the record width of the head, and is executed with the recording medium pressed before and after the record width. Thus, a record-impossible area occurs in the upper and lower margins of the recording medium; preferably the record-impossible areas are small as much as possible. Particularly to form an image by executing horizontal scanning more than once, if an attempt is made to form an image in the vicinity of the upper and lower margins of the recording medium as the normal operation, an area where a 100% image is not provided occurs and also becomes a record-impossible area.
To decrease such areas where a 100% image is not provided, horizontal scanning can be performed more than once without feeding a recording medium in the vertical scanning direction in the upper and lower margins of the recording medium, for example, as described in the Unexamined Japanese Patent Application No. Hei 7-68750, whereby an image is also formed in the upper and lower margins of the recording medium by executing the recording operation more than once, the blank portions of the upper and lower margins of the recording medium can be lessened, and the image-record-possible areas can be widened.
However, if horizontal scanning is performed more than once at the same vertical scanning position at the mode change time or in the upper and lower margins of the recording medium, the same nozzle is used for recording on each line. The nozzles formed on the head vary in characteristics of the liquid jet direction, etc., because of variations in manufacturing the nozzles. The advantage of forming an image in the same area by executing horizontal scanning more than once as described above is that a different nozzle is used in each horizontal scanning for making inconspicuous trouble caused by directivity variations in the nozzles. For example, when the number of print divisions is four, if one nozzle becomes clogged, the print percentage of the clogged nozzle is about 25% per line at the maximum. Therefore, almost normal printing can be executed in the remaining 75%. However, in the image formation method in the related art, horizontal scanning is performed more than once at the same vertical scanning position in the vicinity of the mode change point or in the vicinity of the upper and lower margins of the recording medium. Thus, there is a possibility that inconsistencies in density, a white stripe, etc., will occur as the same line is recorded with the same nozzle.
It is therefore an object of the invention to provide an image formation method, an image formation control system, and an image formation system for reducing degradation of image quality at the mode change time between modes different in print width, such as black and color modes, at the recording time in the upper and lower margins of a recording medium, or the like.
In the invention, just after a first print mode is changed to a second print mode after an image to a mode change point is formed in the first print mode or when recording is executed at the top of an image formation-possible area of a recording medium where an image can be formed, while a move is made in a vertical scanning direction a minute move width at a time smaller than the move width in the vertical scanning direction in the second print mode or an image formation print mode, horizontal scanning is executed a predetermined number of times for forming an image just after the mode change point or at the top of the image formation-possible area, then image formation is executed in the second print mode or the image formation print mode. In such a case, in related art, horizontal scanning is executed a predetermined number of times at the same vertical scanning position, thus inconsistencies in density, white stripes, etc., occur due to manufacturing variations in print elements. In the invention, however, while a move is made in the vertical scanning direction a minute move width at a time, horizontal scanning is executed the predetermined number of times, so that printing the same line with the same print element is eliminated for most lines and occurrence of inconsistencies in density, white stripes, etc., can be suppressed for reducing degradation of image quality.
Likewise, when an image is formed just before change is made from the first print mode to the second print mode or when recording is executed in the end margin of an image formation-possible area of a recording medium where an image can be formed, in the vicinity of the mode change point or in the vicinity of the end margin of the image formation-possible area, while a move is made in the vertical scanning direction a minute move width at a time smaller than the move width in the vertical scanning direction in the first print mode or the print mode applied so far, horizontal scanning is executed a predetermined number of times for forming an image to the mode change point or to the end margin of the image formation-possible area. Thus, while a move is made in the vertical scanning direction a minute move width at a time, horizontal scanning is executed the predetermined number of times, so that printing the same line with the same print element is eliminated for most lines and occurrence of inconsistencies in density, white stripes, etc., can be suppressed for reducing degradation of image quality.